Attention is directed towards instabilities induced in Hydrogen plasmas due to the presence of the desired H- ions. Preliminary investigations indicate that the low density H- beam causes collective instabilities even at very low beam velocities compared to ion acoustic and ion thermal velocities, provided that the non-ideal properties of the background plasma are taken into consideration. The most dangerous instabilities involve oscillations transverse to the direction of beam extraction, and may thereby degrade the beam emittance.